Electronic device manufacturers strive to produce a rich interface for users. Conventional devices use visual and auditory cues to provide feedback to a user. In some interface devices, kinesthetic feedback (such as active and resistive force feedback) and/or tactile feedback (such as vibration, texture, and heat) is also provided to the user, more generally known collectively as “haptic feedback” or “haptic effects.” Haptic feedback can provide cues that enhance and simplify the user interface. Specifically, vibration effects, or vibrotactile haptic effects, may be useful in providing cues to users of electronic devices to alert the user to specific events, or provide realistic feedback to create greater sensory immersion within a simulated or virtual environment.
Haptic feedback has also been increasingly incorporated in portable and mobile electronic devices, such as cellular telephones, smartphones, portable gaming devices, vehicle based devices and interfaces, and a variety of other portable and mobile electronic devices. For example, some portable gaming applications are capable of vibrating in a manner similar to control devices (e.g., joysticks, etc.) used with larger-scale gaming systems that are configured to provide haptic feedback. Further, devices such as those connected to a vehicular power supply may provide haptic feedback over a range of voltage inputs.
In order to generate vibration effects, many devices utilize some type of actuator or haptic output device. Known actuators used for this purpose include an electromagnetic actuator such as a solenoid actuator, an Eccentric Rotating Mass (“ERM”) actuator in which an eccentric mass is moved by a motor, a Linear Resonant Actuator vibration motor (“LRA”), or a piezo transducer. Typically, the power source input voltage for the haptic actuator controls the haptic actuator at a certain current draw. A combination of current and voltage vary the haptic response provided by the actuator. A haptic controller regulates the current provided to the haptic actuator to provide a varying haptic experience based on the desired current level.
Electrical muscle stimulation (“EMS”) uses electrical currents applied in proximity to muscles to cause muscle contractions by stimulating the muscle nerves. The current is applied to the skin, typically through electrodes applied to the skin placed near the muscle to be contracted. Current can be applied to the electrode by a controller using impulses to cause the muscle to quickly contract and relax. EMS has traditionally been used in sports medicine, exercise, and physical therapy.